1. Field of the Invention
The present invention relates to an impurity processing apparatus for doping impurities such as phosphorus, boron, or the like into a semiconductor substrate, etc., or a PSG (PhosphoSilicateGlass) film, a BSG (BoroSilicateGlass) film, or a BPSG (BoroPhosphoSilicateGlass) film, or a carbon film, etc. and to a method for cleaning the impurity processing apparatus.
2. Description of the Prior Art
In recent years, in manufacturing a semiconductor integrated circuit apparatus of superhigh integration, in the case where a p-type or n-type impurity region is formed in a semiconductor substrate, or in the case where an amorphous boron film or an amorphous carbon film is formed for use in absorption of neutron rays, the following methods have been used: an ion injecting method, a plasma doping method using a parallel plate type electrode, a method employing a wave guide for microwaves (xcexc waves) causing ECR (Electron Cyclotron Resonance), or a plasma generating method using a power radiating antenna or the like for generating helicon-plasma, and a plasma CVD (Chemical Vapor Deposition) method using an impurity containing film-forming gas which is converted into a plasma (plasmanized).
FIG. 1 is a side view showing a plasma doping apparatus 101 according to the prior art.
This plasma doping apparatus 101, as shown in FIG. 1, comprises a plasma process part 101A for doping an impurity on a substrate 51 by a plasma gas; and a doping gas supply part 101B having a doping gas source, and a parallel plate type electrode used as a plasma generating source for the plasma process part 101A.
The plasma process part 101A, as shown in FIG. 1, plasmanizes a doping gas and has a process chamber 1 which dopes the substrate 51 by use thereof and can decompress.
The process chamber 1 is connected to an exhaust apparatus 6 through an inducting/ exhausting piping 8a. An upper electrode 2a and lower electrode 2b opposing each other are provided in the process chamber 1, and power is supplied from a power supply 5, i.e., DC (a direct current), AC (an alternating current (frequency 50 Hz or 60 Hz)), LF (low frequency (frequency 100 to 800 kHz) or RF (radio frequency (frequency 1 to 25 MHz)) power, to these electrodes 2a, 2b, and the doping gas is thereby plasmanized. The upper electrode 2a, the lower electrode 2b and the power supply 5 constitute the plasma generating means for plasmanizing the doping gas.
The upper electrode 2a serves as a dispersion member for the doping gas and is provided with a discharge port 3 for the doping gas. The discharge port 3 for the doping gas is connected to a doping gas supply part 101B via piping 8b. 
The lower electrode 2b serves also as a holding base for the substrate 51, and a heater 4 for heating the substrate 51 is provided under the lower electrode 2b. 
Gas bombs 7 for supplying the doping gas are installed in the doping gas supply part 101B. The doping gas is supplied from these gas bombs 7 to the process chamber 1 of the plasma process part 101A through pipings 8c, 8d, 8b. 
In this plasma doping apparatus, if used repeatedly for a long period of time, a decomposed product of a gas containing an element to be doped adheres to an inner wall of a partition surface of the chamber 1 and surfaces of the electrodes 2a, 2b for generating a glow discharge, etc. Such circumstances also occur even in an ion implantation system or a plasma CVD apparatus.
If the insulating decomposed product accumulates on the surfaces of the electrodes 2a, 2b for generating the glow discharge, charge-up occurs to destabilize the glow discharge. Furthermore, in an apparatus using the ECR, a glass surface of a window for introducing xcexc waves into a plasma generating chamber is contaminated, and the decomposed product accumulates even on the inner wall of the plasma generating chamber thereby lowering plasma generating efficiency.
If such a state continues, the discharge becomes unstable and difficult to use. Furthermore, in the worst case, the discharge stops and cannot be used.
Additionally, when a weak p type or n type is doped, the decomposed product containing doping impurities which adhere to the inner wall of the chamber sputter and adhere to the semiconductor substrate, and it becomes difficult to perform lower concentration doping. Accordingly, in order to dope with excellent reproducibility, removal of the decomposed product adhered to the inner wall of the chamber is necessary.
Normally, the following methods are used for cleaning an interior of the chamber of such processing apparatus:
(i) a method glow-discharging for at least an hour in a gas such as argon or hydrogen. As a method for cleaning an inner wall of an ion source housing of an ion implantation system, a method for using hydrogen or an alkyl based substance is disclosed in Japanese Application Laid-Open No. 3-64462, for example.
(ii) a method in which, after a device is disassembled and each part is dipped in a mixture of, for example, a hydrogen peroxide solution and ammonia water, contaminants are manually shaved off by mechanical use of sandpaper or a wire brush, and after cleaning the apparatus, it is reassembled and used.
(iii) a method for cleaning the path of ion beams of the ion implantation system, a method for vaporizing a reaction product adhered to an inner wall, etc. by glow discharge of an oxygen containing gas such as O2, O3 or the like, or a halogen fluoride gas such as CF4, C2F6, NF3 or the like and cleaning is disclosed in Japanese Application Laid-Open No. 4-112441, for example. Furthermore, an example of use of a halogen fluoride gas such as ClF3 or the like is disclosed in Japanese Application Laid-Open No. 8-162433.
However, there are the following drawbacks in a conventional method for cleaning an impurity processing apparatus: Namely, (i) in the method for glow-discharging in a gas such as argon or hydrogen, in the case of argon, an impurity layer adhered to a surface of a silicon substrate is removed, but upon a removal from the surface of the silicon substrate, these impurity atoms invade into the silicon substrate. Furthermore, the material forming the inner wall of the reaction apparatus is sputtered and adheres to the surface of the silicon substrate and invades the substrate, so that it may adversely affect its characteristics.
In the case of hydrogen, for example, when boron is present, a reaction product of boron and hydrogen is generated, and when the reaction chamber is opened to the outside air, diborane is released which is unfavorable for human health. Moreover, if a glow discharge continues for about an hour, a roughness occurs on a surface of the silicon substrate. Furthermore, if the adhered substance starts to be partially removed in the argon or hydrogen, the discharge concentrates on that part and a roughness occurs on the inner wall of the apparatus, the electrode surface and the surface of the silicon substrate. With the other gases, as an adhesive substance is scarcely removed in helium, it is not practical. (ii) the method for disassembling a apparatus and cleaning it chemically with chemicals, or mechanically by a wire brush, etc., takes much labor and time for a slight regulation or recovery of a vacuum after reassembly. Furthermore, a doping impurity element may adhere to a human body or be breathed in, so that this method is inconvenient for reasons of health. (iii) in the method for vaporizing a reaction product adhered to the inner wall, etc., by glow discharge of a halogen fluoride gas such as ClF3, CF4, C2F6 or the like and cleaning, a decomposition product of Cl or F is generated and caution in handling these chemicals is necessary and a great expense is incurred for a public nuisance countermeasure for a rendering harmless this exhaust gas, etc. As the adhesive substance is scarcely removed in the other gases, for example oxygen, it is not practical.
It is an object of the present invention to provide an impurity processing apparatus which has no problems in operability or health in cleaning of the apparatus, and which can be simply cleaned; and a method for cleaning the impurity processing apparatus.
In the impurity processing apparatus of the present invention, a gas containing any one element selected from the group consisting of boron, phosphorus, arsenic, gallium, aluminum, germanium and carbon, or a gas containing a compound of at least one of these elements is used as an impurity-containing gas. Suitable gases include diborane (B2H6), boron trifluoride (BF3), etc., as a compound containing boron (B), phosphine (PH3), etc., as a compound containing phosphorus (P), arsine (AsH3), etc., as a compound containing arsenic (As), trimethylgallium (TMG), etc., as a compound containing gallium (G), trimethylaluminum (TMAl), etc., as a compound containing aluminum (Al), germane (GeH4), germanium tetrafluoride (GeF4), etc., as a compound containing germanium (Ge), and methane (CH4), etc., as a compound containing carbon (C). The impurity-containing gas used in actual practice, the gas containing the element or compound thereof is diluted by hydrogen (H) or helium (He).
In the case where ion injection, doping or a film formation is performed by using such gases, for example, in the case of diborane, a by-product containing boron adheres to an inner wall of a chamber or to a silicon surface.
In the prior art, hydrogen or a halogen fluoride gas has been used as a cleaning gas for removing this byproduct. On the contrary, the present invention is characterized in that plasma of water vapor or a water containing carrier gas is used for removing the by-product. If plasma of water vapor, etc., is used, as compared with the case where hydrogen, etc. are used, the by-product is removed by glow discharging for a period of time of about {fraction (1/10)}. Moreover, a mirror surface of the silicon does not become rough, and it retains its mirror surface state.
In the case where the water vapor, etc., is used, the following reasons explain why the removal rate is 10 times or more higher than the case where hydrogen, etc., is used.
When water is decomposed, it is dissociated into H+ and OH:
H2Oxe2x86x92H++OHxe2x88x92
An impurity adhered after the doping process reacts with these H+ and OHxe2x88x92 ions to form BH, PH, AsH, SbH, etc., and is removed from the inner wall of the chamber. When a plasma luminous spectrum produced by glow discharge in the water vapor is observed, OH in addition to H is observed and simultaneously BH, PH, etc., are seen. Such results indicate that, if OH generates, it reacts with a product containing impurities which adheres to the inner wall, etc., of the process chamber after the doping process, to form a hydride of the impurities.